Attenuation of the locomotor‐sensitizing effects of the D 2 dopamine agonist bromocriptine by either the D 1 antagonist SCH 23390 or the D 2 antagonist raclopride

Injections of the selective D 2 dopamine agonist bromocriptine (5.0 mg/kg, IP) produced progressively stronger locomotion over 10 days of repeated testing. Concurrent treatment with either the D 1 antagonist SCH 23390 (0.01 or 0.1 mg/kg, IP) or the D 2 antagonist raclopride (0.1 or 1.0 mg/kg, IP) suppressed bromocriptine‐induced locomotion on treatment days and attenuated or blocked the progressive increases in locomotion that accompanied repeated injections of bromocriptine alone. The fact that D 1 and D 2 antagonists each block the acute actions of bromocriptine and attenuate the development of bromocriptine sensitization is suggested to imply a striatal rather than a ventral tegmental mechanism for the sensitization produced by repeated treatments with direct dopamine agonists. © 1994 Wiley‐Liss, Inc.